Dog Whistler

The transition from sleep to wakefulness is generally uneventful. That's why mornings like today stand out. I don't know if such a thing is possible but I'd swear I was awakened by the sound of a dog whistling somewhere nearby.

Is it even physiologically possible for a dog to whistle? Or maybe it's certain breeds can do it and others not? And, if it's possible, why do they do it so rarely?  Is it like horses lying down -- a sign that something's wrong?